Good build. I think if you add photos to the warding section it will be better.

Thanks for the suggestion.

I don't think Spell Vamp would really help that much.. but if you do take one, you might as well get a Will of the Ancients for your team.. Hmm.. with all those early points in Vorpal Spikes, I'd think a bit of early Attack Speed would be nice..

Maybe get some 15% CDR item to cap off your CDR, for more frequent uses of Rupture, Feral Scream and Feast.

What spell vamp item should Cho'gath take? I think I will add more AP to the core build and less MR and armor.

I meant to say "you have a problem with 20 MR and NOT a problem with 120 too much armor? o_O

Cho'Gath has a really good base health pool.

beyond about 150 of each resist, spell vamp would be a good investment for tankyness, and that gives you ap as well.

All the more reason to use Aegis of the Legion instead of all that MR AND Armor?

Good build, I do have one suggestion however. Part of being a strong tank is being a real threat to an important carry. If you had a little more AP, then this would be very similar to how I play Cho. Have you thought about a rylais + wits end combo? Cho with a rylais gives him basically a perma-slow since his auto-attacks deal small AoE damage when you get E. Also it gives Cho just a little more powerful CC with his rupture and scream. The slows from rupture and rylais will stack and then your silence will also slow.
But that is just a suggestion.

I think, with that much armor and MR, you become a monster. AS is purely for the fact that Vorpal Spikes hits people in the back too, so it's a lot of damage, in a teamfight.

You realize he has 270 armor right?

Is there a real need for that much MR? ~150 is the ideal amount of MR on a team with 3 casters.. Also.. is there a point of getting Ardor? You don't have enough AS to take real advantage of it and same with your AP.

Seems like a decent build, though, I'm not really a big fan not having the 15 utility for the movement speed.

Much like the way I play Cho. I got 0/9/21, but hey, preference is preference. :D